indicators - led's

[red16v]

Hi, do you really need leds ? why not consider the low voltage (ie 12v) metal base sub miniature bulbs from Maplin - you could spray or paint them whatever colour you want ? on the other hand they also sell 12v coloured subminiature bulbs in a fetching range of 4 colours (also 12v).

Lets say you really want an led. Lets say you go for one with a forward voltage of 2.2v and a forward current of 25mA. The resistor you have to put in series needs to 'drop' a voltage of 12 - 2.2 = 9.8 volts (lets call that 10 volts). The current passing thru the resistor will be the same as the led, ie 25mA (1mA being a 1/1000th of an amp). so, the value of the resistor is (10 divided by 25) then multiplied by 1000, ie 400 ohms. You can't get a resistor of 400 ohm. Get the nearest from maplin which will be 390ohm. You need to get one that will dissipate the heat generated by the current passing thru it - calculated as volts times current. In this case 10volts times 25mA = 250mW (that's a quarter of a watt).

so, If you decided to buy that particular led you would need to buy a 390 ohm resistor at a quarter watt capacity to put in series with the led. Similarly for each led you buy, and don't forget to wire it to the correct side of the supply fuse.

Consider using the conventional bulbs - easier. Regards, yt  

[Sooty and Sweep]

Not wishing to tread on any toes here but...

Maplin supply LEDs that are designed to fit straight onto a 12V supply. I had a couple of these on my old motor wired in to create a 'dummy' alarm system on an old banger.

Maplin Cat no CJ68Y is a 3mm Yellow LED with a built in resistor and are 18p each.

The ones I used were 5mm, red and didn't generate any noticable heat even if they were left on all night....

Or I could be barking up the wrong tree (or just barking!)

[VeeDubGTI16v]

i only wanted to use the led's because they were small and would be easy to mount in the headlights, but the wiring does seem a little confusing.

would i only need one do you reckon in each headlight.

[Sooty and Sweep]

I doubt that one 3mm LED would be anywhere near bright enough.

However for 18p a shot it might be worth getting 5 or 10 from Maplin and wiring them in series and see what happens.

If the 12v ones work (awaiting the blessing of a sparky here...) wire 5 up, rig up a temporary connection and see how it goes. Of course there are things like current drain on the existing circuit to consider but at 8.5 mA per LED, I don't think this would be a problem (again a more qualified electrician should be able to confirm this).

To be honest I had thought about a side repeater made out of LEDs around a VW badge (in the BMW Z4 style ) as I think a ring of LEDs would look quite good as a replacement for a bulb!